Wildfire ash mercury water, New research suggests

New study says the particulate matter released by wildfires can trap mercury and prevent its absorption into local waterways.

“Little is known about the origins, concentration, reactivity, and bioavailability of Hg in residual ash materials in post-fire landscapes,” researchers wrote in a new paper on the subject, published Wednesday in the journal Environmental Science and Technology.

Most studies have focused on the release of mercury into the atmosphere when forests are burned, but as new research confirmed, a significant portion of the emitted mercury can return to the surface via ash. Back on the ground, ash is easily eroded into local waterways, where it collects in various aqueous environs.

When mercury is processed by bacteria, the more toxic methylmercury is produced as a byproduct. Methylmercury can poison fish and other wildlife. Methylmercury poisoning in humans can cause a variety of neurological problems.

But the latest findings suggest wildfire ash may trap mercury, and keep it from taking on more reactive forms.

When a team of researchers tested the levels of mercury found in ash deposited by two recent California forest fires, they found similar concentrations of the toxin in both black ash, produced by low-intensity burning, and white ash, formed during higher-intensity fires.

Both types of ash also contained levels of mercury similar to those measured in unburned vegetation, but their analysis showed mercury attached to ash was more likely to exist in its nonreactive form than mercury found in unburned vegetation.

When researchers allowed ash to mix with water for several days, they found only a small portion of the mercury was absorbed by the water. When unburned vegetation was allowed to soak, a larger percentage of the mercury was released into the water.

“The researchers propose that black carbon, or charcoal, in the ash could bind mercury and keep it in a non-reactive form that is not released into water,” researchers concluded in a news release.